Abstract: The thermal conductivity of solid/liquid aluminum electrolytes, an important parameter for calculating the heat balance of aluminum electrolytic cells, is of great important to predict the thickness change of the solid electrolyte side-ledge on the surface of the sidewall in the electrolysis cell. A new method for determining the thermal conductivity of molten salt was developed by combining thermal analysis sensor measurement with finite element numerical simulation. Under the ANSYS/Fluent soft environment, fluid volume model, discrete coordinate radiative model and melting/solidification model were used to construct the sensor model and simulate its thermal behavior during the cooling process. The residual analysis of the experimental data and simulated data was used as an evaluation standard for the determination of the thermal conductivity of the aluminum electrolyte. The results show that this method is effective for obtaining the thermal conductivities of single-component molten salts and two-component molten salts. In this paper, a piecewise equation for calculating the solid-and-molten-thermal conductivity of NaF-AlF₃ system was established based on the new method. The equation built a relationship between the molecular ratio of NaF/AlF₃ and temperature with the thermal conductivity of solid/liquid state cryolite. The calculated results are in good agreement with the literature data.